This disclosure is generally directed to electrostatographic imaging devices. More specifically, this disclosure is directed to reducing or eliminating the image quality defect known as reload.
In the known process of electrostatographic printing, a charge retentive surface, typically known as a photoreceptor, is electrostatically charged and then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the charge retentive surface while leaving behind an electrostatic image on the non-illuminated surfaces. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image.
Next, the latent image is developed by contacting the latent image to an electrostatically attractable toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the image being produced. The toner image may then be transferred to a substrate or recording medium, and the image is then fixed on the substrate to form a permanent record of the image, or output image. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for copying from an original, or printing electronically generated or stored originals.
In the operation of electrostatographic printing, there arises a defect known as reload. Reload refers to a situation where a roller within a development station fails to properly and completely be reloaded with an appropriate amount of toner after one cycle through the development process in preparation for the next cycle. Reload becomes more and more drastic when a machine engaging in electrostatographic image production is used to produce large quantities of images at high speeds.
U.S. Pat. No. 5,031,570 discloses an apparatus for developing latent electrostatic images on a charge retentive surface with toner. The disclosed apparatus includes a supply of two-component developer having toner and carrier beads, a developer transport structure spaced from the charge retentive surface for conveying developer from the supply of developer to an area opposite the charge retentive surface without contacting the surface, an electrode structure, and a device for establishing an alternating electrostatic field between the developer transport structure and the electrode structure for creating a cloud of toner proximate the electrode structure. The electrode structure can include a plurality of wires operatively connected to an AC power source and positioned in a space between the charge retentive surface and developer transport structure, and a device for creating an electrostatic field between the charge retentive surface and the electrode structure for effecting movement of toner from the cloud of toner to the latent electrostatic images. The transport structure can include a magnetic brush structure having the north and south poles of the brush structure arranged such that the magnetic field is established in the space. This magnetic field does not cause the developer to contact the charge retentive surface. The transport structure can also include a plurality of unbiased wires to agitate the developer on the magnetic brush structure.
U.S. Pat. No. 5,666,619 discloses an apparatus for developing a latent image recorded on a surface. The disclosed device includes a housing defining a chamber storing a supply of developer material, a donor roll spaced from the surface and adapted to transport the developer material to a development zone adjacent the surface, and an electrode wire positioned in the space between the surface and the donor roll. The electrode wire can be electrically biased to detach the developer material from the donor roll to form a cloud of developer material in the space between the electrode wire and the surface with the developer material developing the latent image. The device can also include a wire module providing a device for attaching the ends of the wire and tensioning the electrode wire, and a device for supporting the electrode wire along the length of the wire. The supporting device can be rotatably mounted with respect to the donor roll and located along the donor roll shaft between each end of the donor roll and the donor roll support and having a wire support surface which supports the wire in the vertical direction when the electrode wire is positioned in the space between the surface and the donor roll. The support device can have two support legs separated by an open section, the open section allowing the support device to fit over the donor roll shaft, the two legs of the support device are attached to the housing.
U.S. Pat. No. 5,890,042 discloses an apparatus for developing a latent electrostatic image on a charge retentive surface with toner. The apparatus can include a supply of toner, a donor structure spaced from the charge retentive surface for conveying toner from the supply of toner to an area adjacent the charge retentive surface. The donor structure can have a continuous surface, and a device for applying an alternating current directly to the donor structure to create an alternating electrostatic field between the donor structure and the charge retentive surface to produce a toner cloud adjacent the charge retentive surface for developing the latent electrostatic image thereon.
To reduce reload image quality defects, the voltage across a transport structure can be adjusted based on data regarding toner age, for example. See U.S. patent application Ser. No. 12/634,822. However, the applied voltage range is only effective over a limited range of toner ages. When toner age increases beyond an effective voltage range, the velocity of the transport structure may be manually adjusted to properly compensate and facilitate reducing reload image quality defects. Manual velocity adjustment of the transport structure can still lead to mottle or other image defects at low throughput in high toner age conditions. As the process speed for the image forming apparatus increases, the frequency of occurrence of low toner age conditions will increase. This condition will cause an increase in the need for automated intervention to promote image quality.